Laser production of carbon-13 based on CF2 HCl

ABSTRACT

A method of producing carbon-13 using CF 2  HCl as the feedstock (substrate) material in which the CF 2  HCl is enriched up to a first level of C-13 by I.R. laser photodissociation and then to 90-99% C-13 by a second exchange process. In the preferred arrangement the second stage is a chemical exchange process.

This invention relates to a method for isotope enrichment by laserradiation and more particularly to a method of producing carbon-13 bymultiphoton decomposition of CF₂ HCl.

The use of carbon-13 as an industrial compound is not widespread at thepresent time but is expected to increase. Extensive application ofcarbon-13 to medical screening programs is anticipated. The presentmethod of production is by low temperature distillation of carbonmonoxide and this process is expensive, provides small throughput, needslarge inventory of starting materials, and must be symbiotic with aliquid air plant.

A method of isotopic separation by photopredissociation is described inU.S. Pat. No. 3,983,020, issued Sept. 28, 1976 to C. B. Moore and E. S.Young. A photochemical method for carbon isotopic enrichment isdisclosed in U.S. Pat. No. 4,120,767 issued Oct. 8, 1978 to S. N.Bittenson and P. Houston. This patent describes a process using, as astarting material, a gaseous mixture of at least two isotopic CF₃ Ispecies and irradiating this mixture in a reaction zone with laserradiation at a pressure below about 10 Torr to cause relative enrichmentof one of the species. The enriched residual substrate is ¹³ CF₃ I. Thisprocess is effective but yields are low and therefore production costsare high.

In co-pending U.S. application No. 25,886 filed Apr. 2, 1979 in the nameof Peter A. Hackett, Clive Willis and Michel Gauthier, now abandoned, amethod of producing of carbon-13 by multiphoton dissociation of CF₃ Bror CF₃ Cl is disclosed. In a paper in The Journal of Chemical PhysicsJuly 1, 1979, Vol. 71, No. 1, by Peter A. Hackett, Clive Willis andMichel Gauthier, a method of producing carbon-13 by multiphotondissociation of CF₃ COCF₃ is described.

In co-pending U.S. application No. 132,656, filed Mar. 21, 1980, in thename of Peter A. Hackett, Wing S. Nip and Clive Willis, now U.S. Pat.No. 4,328,078, a method of producing carbon-13 by multiphotondissociation of perfluoropropene (C₃ F₆) is described.

It is another object of the present invention to provide an inexpensivemethod of carbon-13 production.

This and other objects of the invention are achieved by a method ofproducing carbon-13 using CF₂ HCl as the feedstock (substrate) materialin which the CF₂ HCl is enriched up to a first level of C-13 by I.R.laser photodissociation and then to 90-99% C-13 by a second exchange. Inthe preferred arrangement the second stage is a chemical exchangeprocess.

In drawings which illustrate an embodiment of the invention,

FIG. 1 is a block diagram of the two stage process involving chemicalexchange, and

FIG. 2 is a more detailed flow-diagram of the process.

Referring to FIG. 1, an IR laser 10 irradiates a feedstock of CF₂ HCl inreaction chamber 11 to give HCl and CF₂ enriched in C-13. The productsfrom this stage (CF₂ HCl, HCl, C₂ F₄) are passed to separation stage 13where the HCl and the CF₂ HCl (depleted in C-13) are removed. Theremaining component, C₂ F₄ is passed to chemical exchange stage 14 fromwhich a CO₂ product enriched in C-13 is obtained.

Referring to FIG. 2, the feedstock of gaseous CF₂ HCl is irradiated inan appropriate cell 11 by the IR laser 10. The CF₂ HCl is a cheapcommercial substrate and has none of the problems associated withpreviously suggested substrate such as CF₃ I, CF₃ Br, etc. The substratepressure is in the range 10-100 Torr, depending upon laser pulse length.The IR laser operates in the frequency range 1040-1080 cm -1(wavenumbers) with a fluence greater than 5 J cm⁻². The photolysisselectively decomposes the CF₂ HCl and is operated for a sufficient timeto give C₂ F₄ enriched in C-13 to approximately 25-35% along with CF₂HCl and HCl. These products are passed to absorber stage 15 where theHCl is removed and then to freon separation stage 16 where the CF₂ HClwhich is depleted in C-13 is removed. The C₂ F₄ remaining is passed tooxidation stage 17 where it is oxidized to provide a CO₂ product that ispassed to chemical exchange stage 18. This is a CO₂ -carbamate exchangereaction that separated the ¹³ CO₂ and the ¹² CO₂ to give a CO₂ product90-99% C- 13.

We claim:
 1. A method of producing carbon-13 by multiphotondecomposition of CF₂ HCl, said material containing carbon-12 andcarbon-13 isotopic species, comprising:(a) irradiating gaseous CF₂ HClin a reaction chamber at a pressure in the range 10-100 Torr with aninfra-red laser beam at a frequency in the range 1040-1080 wavenumbersto selectively decompose the CF₂ HCl to give C₂ F₄ enriched to a firstlevel of carbon-13, CF₂ HCl, and HCl, (b) passing these products throughan absorber to remove the HCl and a separation stage to remove the CF₂HCl depleted in carbon-13, (c) oxidizing the C₂ F₄ to form CO₂, and (d)passing the CO₂ through a second exchange stage to separate the ¹³ CO₂and the ¹² CO₂ and give a CO₂ product containing approximately 90-99%carbon-13.
 2. A method of producing carbon-13 as in claim 1 wherein theCO₂ is passed through a chemical exchange stage to separate the ¹³ CO₂and the ¹² CO₂ and give a CO₂ product.
 3. A method of producingcarbon-13 as in claim 1 or claim 2 wherein the CF₂ HCl is decomposed togive C₂ F₄ enriched to approximately 25-35% carbon-13.